Thermally powered air diffusers have been widely employed in HVAC systems. The control assembly for such VAV diffusers typically employs a plurality of thermal sensor-actuators and a damper displacing linkage assembly. The sensor-actuators each have a contained wax that expands and contracts with temperature changes and drives a piston. The piston, in turn, is used to displace the linkage assembly that controls the position of the diffuser damper, baffle, disk or blade assembly. Thermally powered VAV diffuser assemblies, for example, are shown in U.S. Pat. No. Re30,953, U.S. Pat. Nos. 4,491,270, 4,509,678, 4,515,069, 4,523,713, 4,537,347, 4,821,955 and 5,647,532.
U.S. Pat. Nos. 4,491,270 and 4,523,713 are typical of VAV diffusers employing three thermal sensor-actuators in the a diffuser in order to be capable of modulating or varying the volume of air flow in both heating and cooling modes. It also will be noted that in both of these patents there is at least one sensor-actuator, the supply air sensor-actuator, which is positioned above the movable damper or disk of the diffuser so as to sense the supply air temperature in the neck of the diffuser. In U.S. Pat. No. 4,491,270, there actually are four sensor-actuators with two supply air sensor-actuators in the neck of the diffuser above a transverse plate which divides the neck elements from the room air sensor-actuators. Moreover, part of the linkage between the sensor-actuators is in the neck of the diffuser above the damper and above the transverse wall between the neck and room air sensor-actuators.
While the diffusers of these patents have operated for many years in commercial settings with only minor maintenance being required, when maintenance is required on the supply air sensor-actuator or portion of the control linkage above the damper, such maintenance can require removal of the diffuser from the supply air conduit for maintenance, repair or replacement.
The thermally-powered VAV diffuser of U.S. Pat. Nos. 4,509,678 and 5,647,532 employ only two sensor-actuator elements in order to power the movement of the damper or diffuser disk. Again, however, one of the sensor-actuators is located above the damper or disk, as is part or most of the control linkage assembly. This makes maintenance and/or replacement of the sensor-actuator and linkage components in the neck of the diffuser more difficult. The VAV diffuser of U.S. Pat. No. 4,509,678 also is not capable of variable air volume (VAV) discharge in both heating and cooling modes. Instead, the linkage assembly controlling damper position is constructed in a manner such that in the heating mode the diffuser damper disk is moved to a pre-adjusted discharge opening and remains at that position.
In U.S. Pat. No. 5,647,532 VAV operation is possible in both heating and cooling modes. While the temperature set point at which the damper opens is not discussed in U.S. Pat. No. 5,647,532, the diffuser of the patent is commercially available from the patent owner, Brian Rickard (Pty) Ltd. The commercially available diffuser has one adjustable temperature set point. Adjustment requires that the control linkage be lowered down out of the diffuser housing to get access to the adjustment, and a single adjustment is all that is provided. Any adjustment of the cooling temperature set point, therefore, also adjusts the heating temperature set point, and visa versa.
Accordingly, it is an object of the present invention to provide a thermally powered control assembly, and a VAV diffuser controlled by such assembly, which has a minimum number of thermal sensor-actuators and yet is capable of VAV operation in heating and cooling modes with independently adjustable set point temperatures for each mode.
A further object of the present invention is to provide a thermally powered VAV diffuser and control assembly therefor in which the thermal sensor-actuators and the linkage assembly which drive the damper for the diffuser are all easily exposed for maintenance, repair and replacement.
Another object of the present invention is to provide a thermally powered VAV diffuser and control assembly therefor that can be biased to a normally open position or can be biased to a normally closed position.
Another object of the present invention is to provide a thermally powered VAV diffuser in which the damper moves to a closed position during change over between heating and cooling modes.
Still another object of the present invention is to provide a thermally powered VAV diffuser and control assembly therefor which has a minimum flow stop assembly that is adjustable and easily accessible.
Another object of the present invention is to provide a thermally powered VAV diffuser in which the damper member can be dropped to a fully open position for system balancing without removing the appearance panel.
Still a further object of the present invention is to provide a thermally powered control assembly for a VAV diffuser which is less complex and accordingly is less costly to manufacture, requires less maintenance and has higher durability.
Another object of the present invention is to provide a thermally powered VAV diffuser assembly which employs a minimum number of thermal sensor-actuators and has independently adjustable set point temperatures which can be easily accessed for adjusting.
Still a further object of the present invention is to provide a VAV diffuser, and control assembly therefor, which has improved room air induction for more accurate sensing of the room air temperature and VAV control.
Still another object of the present invention is to provide an improved damper assembly mounting structure for a VAV diffuser in which the damper is supported by roller bearing elements.
The thermally powered VAV diffuser and control assembly of the present invention have other objects and features of advantage which will become apparent from, and are set forth in more detail in, the accompanying drawing and following the Best Mode of Carrying Out the Invention.